JPH02181526A - Reference station for satellite communication - Google Patents

Abstract

PURPOSE:To obviate an AFC circuit in a slave station by receiving the folding signal of a pilot reference signal based upon a satellite repeater, detecting a frequency variation due to the down link of a communication satellite from the received signal and variably controlling the transmission carrier frequency of a data signal based upon the detected result. CONSTITUTION:When the folding signal PS of the pilot reference signal including a frequency variation f is detected by an AGC amplifier 32 in a modulation circuit part 30, the frequency difference between the folding signal PS including the frequency variation f and a reference oscillation signal F0 (frequency f0) is found out by a 1st mixer 35. The frequency difference signal F1 is added to an oscillation signal FT (frequency fT) generated from a synthesizer 37 by a 2nd mixer 38. The added output signal is supplied to a PSK modulator 40 as a carrier signal F2. When the oscillation output frequency fT of the synthesizer 37 is set up with the relation of the carrier frequency fcar=fT+f0-fP, the frequency of a frequency signal F2 supplied to the PSK modulator 40 goes fcar- f.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a reference station for a satellite communication system that constitutes a star network via a rainy day communication line.

(Prior Art) In recent years, various communication systems using communication satellites have been proposed. Among them, a reference station and multiple slave stations are connected in a star shape via communication satellites, and the base station is connected to each slave station. On the other hand, there are systems that transmit data signals. Figure 4 shows an example of its configuration, where A is the reference station, Bl-B
n indicates a slave station, and S indicates a communication satellite. In the same figure,
The reference station A sends the data signal to, for example, S CP C (Sing
PSK (Phase 5blft Keying
) modulate and transmit. Then, this data signal DT
is relayed by a repeater onboard the communication satellite S to each slave station B.
1 to Bn, and received by these slave stations B1 to Bn, respectively. That is, the data transmitted from the reference station A is transmitted to all slave stations B1 to Bn without fail. The reference station A is also equipped with an oscillator for a pilot reference signal, and constantly transmits a pilot reference signal PIL consisting of an unmodulated carrier signal generated by this oscillator. This pilot reference signal PIL is transmitted to each slave station B1 to B via the communication satellite S in the same way as the data signal DT.
g, respectively. As a result, each slave station Bl
~Bn receives the pilot reference signal PIL and performs AFC (AutosatlcF) based on the received frequency.
The frequency control circuit is operated, thereby correcting downlink frequency fluctuations due to temperature fluctuations in the local oscillation frequency provided in the communication technology 1jJ, S repeaters, satellite Doppler shift, etc. Therefore, even if the satellite downlink frequency changes, the slave stations Bl-Bn can always correctly receive the data signal transmitted from the reference station A.

(Problem to be Solved by the Invention) However, in such a conventional system, fluctuations in the satellite downlink frequency are corrected based on the reception frequency of the pilot reference signal PIL for each slave station B1 to Bn. , all slave stations B1 to Bn must be provided with the AFC circuit for downlink frequency correction. For this reason, the circuit configuration of the slave stations Bl-Bn becomes complicated and expensive, resulting in a reduction in system cost. Since this type of system usually accommodates about 1000 slave stations, an increase in the cost of one slave station has an extremely large effect on the entire system, which is not desirable.

Therefore, the present invention focuses on the above points, and eliminates the need for the AFC circuit for satellite 1i1 downlink frequency correction provided in the slave station, thereby making it possible to easily miniaturize the circuit configuration of the slave station and reduce the system cost. The purpose is to provide a reference station for

[Structure of the Invention] (Means for Solving the Problems) The present invention provides, in addition to means for transmitting a pilot reference signal of a constant frequency to a reference station, a frequency fluctuation detection means 100 as shown in FIG. The frequency fluctuation detection means 100 receives the return signal of the pilot reference signal by the satellite repeater, detects frequency fluctuation due to downlink of the communication satellite from this received signal, and detects the detection result. Based on this, the frequency variable control means 200 variably controls the transmission carrier frequency of the data signal in order to offset frequency fluctuations due to downlink of the communication satellite.

(Function) As a result, according to the present invention, even if the downlink frequency of a communication satellite fluctuates, this frequency fluctuation is detected by the reference station, and the carrier wave frequency of the data signal is variably controlled in order to offset this fluctuation. Therefore, a data signal corrected for the fluctuation in the downlink frequency described above is transmitted to each slave station, and as a result, each slave station always receives the data signal from the reference station reliably without using an AFC circuit. It becomes possible to do so. Therefore, the circuit configuration of each slave station can be easily miniaturized, thereby reducing the system price.

(Embodiment) FIG. 2 is a circuit block diagram showing the main part configuration of a satellite communication reference station in an embodiment of the present invention, in which 10 is a transmitting/receiving device, 20 is an antenna device, and 30 is a modulation circuit in an end station device. Each section is shown below.

The modulation circuit section 30 has an oscillator 31 for generating a pilot reference signal, and the intermediate frequency signal PS of the pilot reference signal generated from the oscillator 31 is transmitted to the transmitting/receiving device 10.
The signal is frequency-converted into a high-frequency signal and amplified with high power, and then transmitted from the antenna device 20 to the communication satellite. This pilot reference signal PIL is relayed by a repeater mounted on a communication satellite, and then transmitted to each slave station Bl-Bn, and also sent back to the reference station. Then, the return signal of this pilot reference signal PIL by the repeater is transmitted to the transmitting/receiving device 1 via the antenna device v120.
After being received at 0 and frequency-converted into an intermediate frequency signal, it is introduced into the modulation circuit section 30 of the terminal equipment.

Incidentally, the modulation circuit unit 30 includes an automatic gain control (AGC) amplifier 32 for detecting the return signal PS' of the pilot reference signal, and a carrier generation circuit 33 for data signal modulation. This carrier wave generation circuit 33 is connected to the above-mentioned AGC.
It has a function of varying the carrier wave frequency based on the frequency of the folded signal PS' output from the amplifier 32,
First, the first mixer 35 detects the frequency difference between the reference oscillation signal FO generated from the reference oscillator 34 and the folded signal PS'. Note that the frequency of the folded signal PS' is equal to the pilot reference signal P generated from the oscillator 31.
The intermediate frequency of S includes the amount of fluctuation in the downlink frequency of the communication satellite. Next, the carrier generation circuit 33 passes the signal F1 representing the frequency difference obtained by the second mixer 35 through the bandpass filter 36 and then introduces it into the second mixing 438, where the signal F1 representing the frequency difference generated by the synthesizer 37 is introduced. Find the frequency sum with the signal FT. This frequency sum signal is passed through a bandpass filter 39 and then supplied to a PSK modulator (MOD) 40 as a carrier signal F2. This PSK modulator 40 performs PSK modulation on the carrier signal F2 according to the transmission data SD, and this modulated data signal is frequency-converted in the transmitting/receiving device 10 and further amplified with high power, and then sent from the antenna device 20 to the communication satellite. will be sent.

Because of this configuration, if the downlink frequency of the communication satellite changes by Δf due to a temperature change in the relay local oscillation frequency of the communication satellite or a satellite Doppler shift, this frequency will change as shown by the solid line O in Figure 3. Fluctuation amount Δf
The return signal PS' of the pilot reference signal containing
frequency fP+Δf) of the AGC amplifier 3 of the modulation circuit section 30
Detected by 2. Then, this frequency fluctuation amount Δ
The frequency difference (fo − (fp + Δf)) between the folded signal PS′ containing f and the reference oscillation signal FO (frequency fo) is the first
This frequency difference signal F1 is added to the oscillation signal FT (frequency fT) of the synthesizer 37 in the second mixer 38. This addition output signal is then supplied to the PSK modulator 40 as a carrier wave signal F2.

That is, the PSK modulator 40 has fT+(fo　(fp+Δf)1 −fT+fO−fp−Δf A carrier wave signal F2 having a frequency of 1 is supplied.

Now, the oscillation output frequency f of the synthesizer 37 is
T is fear−fT+ for the carrier frequency f ear
If the relationship is set in advance such that f(1-fp), the frequency of the carrier signal F2 supplied to the PSK modulator 40 will be f car-Δf, which is the normal carrier frequency. The frequency is lower than f car by the variation Δf of the downlink frequency.

Therefore, at this time, the PSK modulator 40 outputs a modulated data signal whose center frequency has been corrected in advance to become lower as shown by the broken line @ in FIG. 3 according to the carrier wave F2. Therefore, when each slave station Bl-Bn receives the modulated data signal, a modulated data signal with a center frequency f ear as shown by the solid line 0 in FIG. 3 is obtained, and for each slave station Bl-Bn, This is equivalent to receiving a data signal with no downlink frequency fluctuations. Therefore, each slave station Bl-Bn can always receive data signals stably.

Note that even if frequency control is performed as described above, each slave station Bl
The carrier frequency of the data signal at -Bn may vary somewhat. However, since the demodulators of the slave stations B1 to Bn generally have a supplementary function for small fluctuations in the carrier wave frequency, the above-mentioned small fluctuations in the carrier wave frequency can be absorbed by this supplementary function.

As described above, in this embodiment, the reference station itself receives the feedback signal from the communication satellite of the pilot reference signal transmitted by the reference station, and transmits the data signal based on the received signal frequency to cancel out the variation in the satellite downlink frequency. By variable control of the carrier wave frequency, even if the satellite downlink frequency fluctuates due to temperature fluctuations in the local oscillation frequency of the satellite transponder or satellite Doppler shift, each slave station always has the same level of control as if there were no fluctuations in the satellite downlink frequency. It is possible to receive data signals from the reference station under the same conditions. Therefore, the AFC circuit of each slave station is not required, and thereby the circuit configuration of the slave station can be easily downsized. Also,
This allows the system price to be reduced.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, variable control of the carrier wave frequency of the data signal was performed in the intermediate frequency signal range in the terminal equipment.
The transmitting/receiving device may perform this in a high frequency range. In addition, the circuit configuration of the means for detecting fluctuations in the satellite downlink frequency and the variable carrier frequency control means can be modified in various ways without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, the reference station is provided with a frequency fluctuation detection means and a frequency variable control means in addition to a means for transmitting a pilot reference signal of a constant frequency, The detecting means receives a return signal of the pilot reference signal described in 1- by the Ugetsu repeater, and detects frequency fluctuations due to downlink of the communication satellite from this received signal,
Based on this detection result, the frequency variable control means variably controls the transmission carrier frequency of the data signal in order to offset frequency fluctuations due to downlink of the communication satellite. It is possible to eliminate the need for an AFC circuit for correction, thereby providing a reference station for satellite communication in which the circuit configuration of the slave station can be easily miniaturized and the system cost can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram showing the configuration of a satellite communication reference station according to the present invention, FIG. 2 is a circuit block diagram showing the main part configuration of a satellite communication reference station according to an embodiment of the present invention, and FIG. 3 is its operation. FIG. 4 is a diagram showing an example of a carrier wave frequency used for explanation, and is a schematic configuration diagram showing an example of a satellite communication system. A... Reference station, Bl-Bn... Slave station, S... Communication satellite, 10... Transmitting/receiving device, 20... Antenna device, 30... Modulation circuit section of terminal station device, 31... - Oscillator for pilot reference signal generation, 32... Automatic gain control (AGC) amplifier, 33... Carrier wave generation circuit, 34.
...Reference oscillator, 35...First mixer, 36.39
...Bandpass filter, 37...Synthesizer, 3
8... Second mixer, 40... PSK modulator, PI
L...Pilot reference signal, DT...Data signal. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (1)

[Claims] In a satellite communication system in which a data signal is transmitted from a reference station, this data signal is relayed by a repeater of a communication satellite, and transmitted to each of a plurality of slave stations, there is provided a means for transmitting a pilot reference signal of a constant frequency; a frequency fluctuation detection means for receiving a return signal from the repeater and detecting a frequency fluctuation due to the downlink of the communication satellite from the received signal; 1. A reference station for satellite communication, comprising: variable frequency control means for variably controlling the transmission carrier frequency of the data signal in order to offset fluctuations.